Conventionally, in an image forming apparatus, a sheet size detection mechanism is used so that sizes of sheets that are accommodated in a sheet supply cassette are recognized on an apparatus main body side.
The conventional sheet size detection mechanism includes a signal output drum provided in the sheet supply cassette. The signal output drum includes a plurality of projections in an axial direction thereof. In addition, a plurality of detection levers are located in the apparatus main body to which the sheet supply cassette is installed to face the plurality of projections of the signal output drum (see JP Laid-Open Patent Application No. H8-34525 (e.g. see columns 0013, 0014, FIGS. 6 and 7).
However, in the above-discussed conventional art, since the plurality of projections and the plurality of detection levers are each arranged in the axial direction of the signal output drum, when a setting number of the sheet sizes increases, a size of the signal output drum in the axial direction needs to increase, which results in the prevention of downsizing of the apparatus main body.